The processing power of CPUs, and the computer systems that contain them, has continued to double on the average of every two years over the past twenty years. However, the performance of mass storage devices and computer bus interconnections between mass storage devices and CPUs has not increased at the same rate. As a result, many modern computer systems may be limited in processing speed by the speed at which data can be accessed and transported between memory and peripheral devices, such as hard disk drives. In addition, computer systems may be limited by the amount of data that they can efficiently access.
The small computer system interface ("SCSI") bus is the most widespread and popular computer bus for interconnecting mass storage devices, such as hard disks and CD-ROM drives, with the memory and processing components of computer systems. Depending on the particular SCSI standard to which the SCSI bus is implemented, the SCSI bus may interconnect 7, 15, or 31 different mass storage devices with an internal bus within a computer system, and may transfer data at rates of from 2 megabytes ("Mbytes") per second up to 40 Mbytes per second. Because the internal buses within computer systems can generally accommodate only a small number of SCSI bus interconnections, the SCSI bus architecture imposes significant limitations in the amount of data that can be accessed by a computer system as well as a significant limitation in the rate at which data can be transferred between a mass storage device and a computer system.
The Fibre Channel ("FC") architecture and protocol for data communications has been developed in order to overcome the limitations imposed by the SCSI bus architecture. When optical fibres are employed as a physical medium for interconnecting computer systems and mass storage devices, a FC network can extend for ten kilometers and can transfer data between a computer system and a mass storage device at up to 200 Mbytes per second. Whereas the SCSI bus supports connection of up to 31 target devices, a FC network can support connection of more than 16,000,000 target devices.
Although the FC technology greatly expands the amount of data that can be accessed by a computer system and increases the potential data transfer rate between a computer system and a mass storage device, computer systems continue to include mass storage devices compatible only with the SCSI bus, for both economical and practical reasons. As a result, computer users, system designers, and computer system administrators desire to incorporate the FC technology as a backbone communications mechanism within their computer systems, while continuing to use SCSI compatible mass storage devices. For this reason, a number of computer hardware vendors have produced FC/SCSI-bus multiplexers that contain one or more FC host adapters interconnected to a number of SCSI-bus adapters that each control a different SCSI bus.
While current FC/SCSI-bus multiplexers provide system designers with the ability to interconnect a computer system with many more mass storage devices, current FC/SCSI-bus multiplexers have not achieved greatly improved data transfer rates to and from the mass storage devices. A need has therefore been recognized in the computing industry for a high-performance FC/SCSI-bus multiplexer architecture that will allow FC/SCSI-bus multiplexers to provide a sufficiently efficient flow of data between mass storage devices and remote computers accessing those mass storage devices through FC connections to better realize, in practice, the greatly increased connectivity, data accessibility, and data transfer rate theoretically provided by the FC technology.